CN112261990B

CN112261990B - Hydrophilic porous membrane and method for producing hydrophilic porous membrane

Info

Publication number: CN112261990B
Application number: CN201980039713.XA
Authority: CN
Inventors: 石井阳大; 三井哲朗; 梅原健志
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2018-06-15
Filing date: 2019-06-14
Publication date: 2022-11-29
Anticipated expiration: 2039-06-14
Also published as: CN112261990A; US20210086139A1; WO2019240254A1; JPWO2019240254A1; JP7124074B2

Abstract

According to the present invention, there is provided a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose (preferably hydroxypropyl cellulose) having a weight average molecular weight of 10,000 or more and less than 110,000 retained in the porous membrane. The hydrophilic porous membrane of the present invention has high water permeability and can pass an integrity test when used as a filtration membrane of a filter cartridge. Also, the present invention provides a method for producing the hydrophilic porous membrane, comprising a step of allowing a hydrophilizing liquid containing 0.005 to 0.500 mass% of hydroxyalkyl cellulose having a weight average molecular weight of 10,000 or more and less than 110,000 to permeate the porous membrane.

Description

Hydrophilic porous membrane and method for producing hydrophilic porous membrane

Technical Field

The present invention relates to a hydrophilic porous membrane and a method for producing the hydrophilic porous membrane.

Background

Porous membranes made of polymers are industrially useful as filtration membranes for water purification and the like, and are also commercially available as pleated sleeves which are collected in a certain capacity. In general, a completeness test is performed on the filter cartridge in order to confirm the presence or absence of defects such as pinholes or poor sealing. In the integrity test, pressure was applied after water was passed through a filter membrane installed in a filter to fill pores with water and gas leakage was observed. In this case, if the filter membrane is not wetted with water and has pores not blocked with water, gas leaks even if there are no pinholes when pressure is applied, and the integrity cannot be determined. That is, if the filtration membrane is hydrophobic, it is difficult to accurately confirm the presence or absence of defects by the integrity test. In particular, in the filter cartridge, both ends of the filter membrane wound in a cylindrical shape are welded to a plate called an end plate, but it is difficult to completely wet the vicinity of the welded portion, and even if there is no defect, the filter membrane is likely to be defective in a completeness experiment.

Patent document 1 discloses the following: hydrophilic polymer is applied in advance as a wetting agent only to both ends of the porous membrane to be the welded portion, and wettability of the welded portion is ensured when the porous membrane is assembled to the sleeve.

Patent document 2 discloses a microfiltration porous membrane that is obtained by providing a polyethersulfone membrane with a hydrophilic polymer and that can be subjected to autoclave sterilization treatment. In the production of the microfiltration porous membrane described in patent document 2, hydroxypropyl cellulose having a molecular weight of 110,000 to 150,000 is used as the hydrophilic polymer.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2003-320230

Patent document 2: japanese patent laid-open No. 2003-251152

Disclosure of Invention

Technical problem to be solved by the invention

The present invention addresses the problem of providing a porous membrane as a substrate, which has improved hydrophilicity and hydrophilicity, and a method for producing the same. In particular, an object of the present invention is to provide a hydrophilic porous membrane that can pass an integrity test and has high water permeability when used as a filtration membrane of a filter cartridge, and a method for producing the same.

Means for solving the technical problem

The present inventors have conducted extensive studies to solve the above problems, and have found that a hydrophilic porous membrane produced using a specific hydrophilic polymer gives accurate results in an integrity test and has high water permeability, thereby solving the above problems.

That is, the present invention provides the following < 1 > to < 14 >.

< 1 > a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose held by the porous membrane, the hydroxyalkyl cellulose having a weight average molecular weight of 10,000 or more and less than 110,000.

< 2 > the hydrophilic porous membrane according to < 1 > wherein,

the porous membrane has a structure having a pore size distribution in the thickness direction and an asymmetric pore size distribution in the thickness direction.

< 3 > the hydrophilic porous membrane according to < 1 > or < 2 > wherein,

the hydroxyalkyl cellulose has a weight average molecular weight of 10,000 to 100,000.

< 4 > the hydrophilic porous membrane according to any one of < 1 > to < 3 >, wherein,

the content of the hydroxyalkyl cellulose is 0.05 to 3% by mass based on the mass of the hydrophilic porous membrane.

< 5 > the hydrophilic porous membrane according to any one of < 1 > to < 3 >, wherein,

the content of the hydroxyalkyl cellulose is 0.1 mass% or more and less than 0.5 mass% with respect to the mass of the hydrophilic porous membrane.

< 6 > the hydrophilic porous membrane according to any one of < 1 > to < 5 >, wherein,

the hydroxyalkyl cellulose is hydroxypropyl cellulose.

< 7 > the hydrophilic porous according to any one of < 1 > to < 6 >, wherein,

the porous membrane contains polysulfone.

< 8 > the hydrophilic porous membrane according to < 7 > wherein,

the porous film retains polyvinylpyrrolidone.

< 9 > the hydrophilic porous membrane according to any one of < 1 > to < 8 >, wherein,

the hydroxyalkyl cellulose is retained on the entire surface of the porous membrane.

< 10 > the hydrophilic porous membrane according to any one of < 1 > to < 8 >, wherein,

the porous film is in the form of a long sheet, and the hydroxyalkyl cellulose is held only at both ends on the long side.

< 11 > a method for producing the hydrophilic porous membrane described in any one of < 1 > to < 9 >, the method comprising:

and a step of allowing a hydrophilization solution containing 0.005 to 0.500 mass% of the hydroxyalkyl cellulose to permeate the porous membrane.

< 12 > the production method according to < 11 >, wherein,

the penetration is performed by immersing the entire porous membrane in the hydrophilizing liquid.

< 13 > the production process according to < 12 >, wherein,

the immersion is carried out for 30 seconds or less.

< 14 > a method for producing the hydrophilic porous membrane < 10 > comprising:

and applying a hydrophilizing solution containing 0.005 to 0.500 mass% of the hydroxyalkyl cellulose to both ends on the long side.

Effects of the invention

According to the present invention, a hydrophilic porous membrane having improved hydrophilicity of a porous membrane as a base material and a method for producing the same are provided. The hydrophilic porous membrane of the present invention can pass a complete test of a cartridge and has high water permeability.

Detailed Description

The present invention will be described in detail below.

In the present specification, "-" is used in the meaning including numerical values described before and after the term "lower limit value" and numerical values described after and after the term "upper limit value".

< hydrophilic porous Membrane >

In the present specification, the hydrophilic porous membrane refers to a membrane in which a porous membrane as a base is hydrophilized. The hydrophilic porous membrane refers to a membrane in which hydrophilicity is increased by retaining hydroxyalkyl cellulose relative to a porous membrane as a substrate, and does not mean that the porous membrane as a substrate is completely hydrophobic.

The hydrophilic porous membrane is a membrane having a plurality of pores. The pores can be confirmed by, for example, a Scanning Electron Microscope (SEM) image or a Transmission Electron Microscope (TEM) image of the cross section of the film.

The hydrophilic porous membrane of the present invention comprises a porous membrane and hydroxyalkyl cellulose retained in the porous membrane.

The term "held in the porous membrane" means that the hydrophilic porous membrane is bonded to the porous membrane to such an extent that the hydrophilic porous membrane is not easily peeled off during storage or use. The porous membrane and the hydroxyalkyl cellulose may also be bonded to each other by, for example, hydrophobic interaction.

The hydroxyalkyl cellulose may also be maintained in a state of coating at least a portion of the outer surface of the porous membrane. In the present specification, the outer surface of the porous membrane refers to the membrane surface (front or back surface of the membrane) of the porous membrane and the surface of the porous membrane facing each pore inside the porous membrane (in the present specification, it may be referred to as "pore surface"). In the porous film, either one film surface may be coated, or both film surfaces may be coated. In the hydrophilic porous membrane of the present invention, when the pores coated inside are part of the plurality of pores inside the porous membrane, the part thereof may be, for example, the vicinity of any one membrane surface of the porous membrane. The film surface at this time is preferably a coated film surface. Most preferably, the surface of the porous film (both the front and back surfaces of the film) and the entire surface of the pores are coated.

The hydrophilic porous membrane of the present invention may have hydroxyalkyl cellulose held over the entire surface, or may have hydroxyalkyl cellulose held only in a part thereof. By holding over the entire surface, hydrophilization of the entire porous film can be preferably achieved. Further, hydrophilization can be achieved within a necessary range by making use of the properties of the porous film as a base material by hydrophilizing only a portion where hydrophilicity is particularly required.

As the hydrophilic porous membrane of the present invention only in a part of the holding of hydroxyalkyl cellulose examples preferably cited only in long sheet shaped porous membrane long side of both ends of the hydrophilic porous membrane holding hydroxyalkyl cellulose. When both ends on the long side are porous membranes having a short side of 20 to 35cm, for example, the length may be from the edge of the long side of the hydrophilic porous membrane to a position within 4cm, more preferably 2cm, in the short side direction. When the porous membrane is used as a filtration membrane of a filter cartridge, a load is easily applied to both ends. That is, a long sheet-like porous film is pleated as necessary, wound into a cylindrical shape, and the aligned portions are sealed, and then both end portions of the cylindrical shape are welded to a plate called an end plate of a sleeve. When welded, porous membranes are hydrophobized by the application of heat and are prone to gas leakage during integrity testing. In particular, by increasing the hydrophilicity at both ends to which heat is applied by holding hydroxyalkyl cellulose, a hydrophilic porous membrane capable of preventing a decrease in hydrophilicity due to a sleeve production process can be obtained, and a filter cartridge that passes an integrity test can be produced using the hydrophilic porous membrane.

Therefore, as for the long sheet-like porous membrane, particularly, the long sheet-like porous membrane used as a filtration membrane of a filter cartridge preferably has hydroxyalkyl cellulose held at both ends at least on the long side.

In the hydrophilic porous membrane of the present invention, the hydroxyalkyl cellulose may be held substantially uniformly over the entire membrane thickness direction or may be held partially in the membrane thickness direction in the portion holding the hydroxyalkyl cellulose, but it is preferable to hold the hydroxyalkyl cellulose substantially uniformly in the membrane thickness direction.

[ porous film ]

(Structure of porous Membrane)

In the present specification, a porous membrane is a membrane that is a substrate of a hydrophilic porous membrane.

The porous film refers to a film having a plurality of pores. The pores can be confirmed by, for example, a Scanning Electron Microscope (SEM) image or a Transmission Electron Microscope (TEM) image of the cross section of the film.

The pore diameter of the pores of the porous membrane may be appropriately selected depending on the size of the object to be filtered, and may be 0.01 to 25 μm, and more preferably 0.03 to 20 μm. When having a pore size distribution, it may be distributed within this range. The pore diameter may be measured from a photograph of a cross section of the membrane obtained by an electron microscope. The porous membrane is cut with a microtome or the like, and a photograph of the cross section of the porous membrane can be obtained as a slice of a thin film that can be observed in the cross section.

The pore diameter of the pores of the hydrophilic porous membrane can be made smaller than that of the porous membrane of the substrate by retaining the hydroxyalkyl cellulose, but can be generally approximated to the pore diameter of the porous membrane.

The porous membrane may have a pore size distribution in the thickness direction or may have a homogeneous structure having no pore size distribution in the thickness direction, but a structure having a pore size distribution in the thickness direction is preferable. In the structure having a pore size distribution in the thickness direction, it is preferable that the structure has an asymmetric structure (asymmetric structure) in the thickness direction in which the pore size distribution is different between the pore size on the front surface and the pore size on the back surface of the membrane. The same applies to the hydrophilic porous membrane. Examples of the asymmetric structure include a structure in which the pore diameter continuously increases in the thickness direction from one membrane surface toward the other membrane surface, a structure in which a dense portion having a layer shape with the smallest pore diameter is provided inside, and the pore diameter continuously increases in the thickness direction from the dense portion toward at least one membrane surface of the porous membrane, and the like.

In particular, the porous membrane preferably has the following structure: the porous membrane has a layered dense site having the smallest pore diameter inside, and the pore diameter continuously increases from the dense site toward at least one membrane surface of the porous membrane in the thickness direction.

In this specification, when comparing the pore diameters of the membranes in the thickness direction, SEM photographs of the membrane sections divided in the thickness direction of the membranes were taken. The number of divisions can be appropriately selected according to the thickness of the film. The number of divisions is at least 5 or more, and for example, 20 divisions from the surface X described later are made in a 200 μm thick film for comparison. The size of the division width is a width in the thickness direction of the film, and does not mean a width in a photograph. In the comparison of the pore diameters in the thickness direction of the membrane, the pore diameters are compared as the average pore diameter of each partition. The average pore diameter of each partition may be, for example, an average of 50 pores in each partition in a membrane sectional view. The film cross-sectional illustration at this time can be obtained, for example, with a width of 80 μm (a distance of 80 μm in a direction parallel to the surface). In this case, for the partition having a large hole and in which 50 cells cannot be measured, the number of cells that can be obtained in the partition may be measured. At this time, if the hole is large and is not accommodated in the partition, the size of the hole is measured in another partition.

The layer-like dense portion having the smallest pore diameter means a layer-like portion of the porous membrane corresponding to the partition having the smallest average pore diameter among the partitions of the membrane cross section. The dense site may be constituted by a site corresponding to 1 partition, or may be constituted by sites corresponding to 2, 3, or the like, which have an average pore diameter within 1.1 times the average pore diameter of the partition having the smallest average pore diameter. The thickness of the dense part may be 0.5 to 50 μm, and preferably 0.5 to 30 μm. In the present specification, the average pore diameter of the dense sites is defined as the minimum pore diameter of the porous membrane. The minimum pore diameter of the porous membrane is preferably 0.01 μm or more, more preferably 0.02 μm or more, and preferably 10 μm or less, more preferably 5 μm or less. Here, the average pore diameter of the dense site is determined by ASTM F316-80.

The porous membrane preferably has dense sites inside. By interior is meant not in contact with the surface of the membrane and by "having dense sites within" is meant that the dense sites are not partitions closest to either surface of the membrane. By using a porous membrane having a structure in which dense sites are present inside, the permeability of a substance intended to permeate the porous membrane is less likely to decrease than in the case where a porous membrane having dense sites in contact with the surface is also used. Although not being bound by any theory, it is thought that this is because adsorption of the above-mentioned substance or other substances is not easily caused by having dense sites inside.

The dense portion is preferably located on either surface side of the central portion of the thickness of the porous film. Specifically, the dense portion is preferably located at a distance of 2 minutes or less, more preferably 3 minutes or less and still more preferably 4 minutes or less and 1 minute or less from any surface of the porous film in the thickness of the porous film. The distance may be determined from the photograph of the cross section of the film. In the present specification, the surface of the porous membrane on the side closer to the dense site is referred to as "surface X".

Preferably, in the porous film, the pore diameter continuously increases from the dense site toward at least one surface in the thickness direction. In the porous membrane, the pore diameter may continuously increase from the dense portion toward the surface X in the thickness direction, the pore diameter may continuously increase from the dense portion toward the surface on the opposite side to the surface X in the thickness direction, or the pore diameter may continuously increase from the dense portion toward any one surface of the porous membrane in the thickness direction. Of these, the pore diameter preferably continuously increases at least from the dense site toward the surface on the opposite side to the surface X in the thickness direction, and more preferably also continuously increases from the dense site toward any surface of the porous membrane in the thickness direction. The phrase "the pore diameter continuously increases in the thickness direction" means that the difference in the average pore diameter between the partitions adjacent to each other in the thickness direction is 50% or less, preferably 40% or less, and more preferably 30% or less of the difference between the maximum average pore diameter (maximum pore diameter) and the minimum average pore diameter (minimum pore diameter). By "continuously increasing" is meant essentially a site where there is no decrease and an increase is uniform, but may occasionally produce a decrease. For example, when 2 partitions are combined from the surface, the average value of the combination uniformly increases (uniformly decreases from the surface toward the dense site), and it can be determined that "the pore diameter continuously increases from the dense site toward the surface of the membrane in the thickness direction".

The maximum pore diameter of the porous membrane is preferably 0.1 μm or more, more preferably 1.5 μm or more, and is preferably 25 μm or less, more preferably 23 μm or less, more preferably 21 μm or less. In the present specification, the average pore diameter of the partition having the largest average pore diameter among the partitions of the membrane cross section is defined as the maximum pore diameter of the porous membrane.

The ratio of the average pore diameter of the dense portion to the maximum pore diameter of the porous membrane (the ratio of the minimum pore diameter to the maximum pore diameter of the porous membrane, and the value obtained by dividing the maximum pore diameter by the minimum pore diameter, which may also be referred to as "anisotropy ratio" in the present specification) is preferably 3 or more, more preferably 4 or more, and further preferably 5 or more. The reason is to increase the average pore diameter except for the dense sites and to improve the substance permeability of the porous membrane. The anisotropy ratio is preferably 25 or less, and more preferably 20 or less. This is because the effect of the multi-stage filtration can be obtained with high efficiency in the range of the anisotropy ratio of 25 or less.

The partition in which the average pore diameter becomes the largest is preferably a partition closest to or in contact with either surface of the membrane.

In the partition closest to either surface of the membrane, the average pore diameter is preferably more than 0.05 μm and 25 μm or less, more preferably more than 0.08 μm and 23 μm or less, and still more preferably more than 0.1 μm and 21 μm or less. The ratio of the average pore diameter of the partition closest to any one surface of the membrane to the average pore diameter of the dense part is preferably 1.2 or more and 20 or less, more preferably 1.5 or more and 15 or less, and still more preferably 2 or more and 13 or less.

The thickness of the porous membrane is not particularly limited, but is preferably 10 to 1000 μm, more preferably 10 to 500 μm, and still more preferably 30 to 300 μm from the viewpoints of membrane strength, handling properties, and filtration performance.

The hydroxyalkyl cellulose is held, so that the thickness of the hydrophilic porous membrane can be larger than that of the porous membrane of the substrate, but is generally substantially the same as that of the porous membrane.

(composition of porous Membrane)

The porous membrane contains a polymer. The porous membrane is preferably composed essentially of a polymer. The number average molecular weight (Mn) of the polymer is preferably 1,000 to 10,000,000, more preferably 5,000 to 1,000,000.

Examples of polymers include thermoplastic and thermosetting polymers. Specific examples of the polymer include polysulfone, sulfonated polysulfone, polyethersulfone (PES), sulfonated polyethersulfone, cellulose acylate, nitrocellulose, polyacrylonitrile, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, polycarbonate, organosiloxane-polycarbonate copolymer, polyester carbonate, organopolysiloxane, polyphenylene ether, polyamide, polyimide, polyamideimide, polybenzimidazole, ethylene-vinyl alcohol copolymer, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polyvinyl fluoride, polyethylene terephthalate, polyamide, polyimide, 6,6-nylon, and polyvinylidene fluoride (PVDF). These may be homopolymers, copolymers, polymer blends, or polymer alloys from the viewpoints of solubility, optical properties, electrical properties, strength, elasticity, and the like.

Among these, polysulfone, polyethersulfone, PVDF, sulfonated polysulfone, sulfonated polyethersulfone, 6,6-nylon, and cellulose acylate are preferable, and polysulfone is more preferable.

The porous film may contain other components than the polymer as additives.

Examples of the additive include salt, metal salts of inorganic acids such as lithium chloride, sodium nitrate, potassium nitrate, sodium sulfate, and zinc chloride, metal salts of organic acids such as sodium acetate and sodium formate, polymers such as polyethylene glycol and polyvinylpyrrolidone, polymer electrolytes such as sodium polystyrene sulfonate and polyvinyl benzyl trimethyl ammonium chloride, and ionic surfactants such as sodium dioctyl sulfosuccinate and sodium alkylmethyltaurate. The additive may act as an expanding agent for the porous structure.

For example, when polysulfone or polyethersulfone is used as the polymer, the porous membrane preferably further contains polyvinylpyrrolidone. In this case, the polyvinylpyrrolidone may be in a state of being held in the porous film. Polysulfone or polyethersulfone, which are hydrophobic, are rendered hydrophilic by the inclusion of polyvinylpyrrolidone. Polyvinylpyrrolidone is added as a pore former to a solution for forming a polysulfone film or a polyethersulfone film as described in, for example, japanese patent application laid-open No. Sho 64-034403. Most of the polyvinylpyrrolidone in the film-forming dope was dissolved in the coagulation water and removed during the film-forming process, but a part of the polyvinylpyrrolidone remained on the film surface.

The porous film is preferably a film formed of one composition as a single layer, and is preferably not a multilayer laminated structure.

As a method for producing a porous membrane, reference can be made to Japanese patent application laid-open No. 4-349927, japanese patent publication No. 4-068966, japanese patent application laid-open No. 04-351645, japanese patent application laid-open No. 2010-235808, and the like.

Commercially available porous films can be used. Examples thereof include Sumilite FS-1300 (manufactured by Sumitomo Bakelite Co., ltd.), micro PES 1FPH (manufactured by Membrana GmbH), PSEUH20 (manufactured by polysulfone membranes, FUJIFILM Co., ltd.), durapore (PVDF membrane, manufactured by Merkmillipore Co., ltd.), 15406 (PES membrane, manufactured by Sartorius Co., ltd.), and the like.

[ hydroxyalkyl cellulose ]

The hydroxyalkyl cellulose in the hydrophilic porous membrane of the present invention is a hydrophilic polymer for hydrophilizing the porous membrane.

The hydrophobicity of the cellulose skeleton of the hydroxyalkyl cellulose contributes to hydrophobic interaction with the porous membrane as a substrate, and hydrophilicity can be imparted to the porous membrane by the hydroxyl group or the hydroxypropyl group of the side chain of the hydroxyalkyl cellulose while being retained in the porous membrane. Furthermore, since the hydroxyalkyl cellulose has a high intermolecular force, it is presumed that the molecules strongly interact with each other in the hydrophilic porous film and can retain the form thereof.

Furthermore, hydroxyalkyl cellulose is an ingredient that can be used as a food additive, and therefore, there is no need to rinse after manufacturing the filter cartridge. Therefore, a safe hydrophilic porous membrane with less process burden can be obtained.

The hydroxyalkyl cellulose may have a weight average molecular weight of 10,000 or more and less than 110,000, preferably 10,000 or more and 100,000 or less, more preferably 10,000 or more and less than 100,000, still more preferably 10,000 or more and 80,000 or less, and most preferably 30,000 or more and 50,000 or less. In the present specification, the weight average molecular weight means a molecular weight measured by GPC (gel permeation chromatography), and specifically, may be measured under the procedure and conditions described in the examples in the present specification.

By setting the weight average molecular weight of the hydroxyalkyl cellulose to less than 110,000, the hydroxyalkyl cellulose is less likely to aggregate. Therefore, clogging due to hydroxyalkyl cellulose is hardly caused, and a decrease in water permeability of the hydrophilic porous membrane can be prevented. Further, by setting the content to 10,000 or more, the hydroxyalkyl cellulose is retained in the porous membrane, and thus the interaction between the hydroxyalkyl celluloses and the interaction between the hydroxyalkyl cellulose and the porous membrane are sufficient.

The hydroxyalkyl cellulose is preferably a cellulose to which an alkylene oxide having 3 to 5 carbon atoms has been added. This is because the interaction between the porous membrane and the hydroxyalkyl cellulose and the hydrophilicity of the hydrophilic porous membrane obtained are obtained in a range preferable for practical use. Most preferred is hydroxypropylcellulose obtained by adding propylene oxide (having 3 carbon atoms) to cellulose. When the number of addition (degree of substitution) of alkylene oxide is large, hydrophilicity increases, whereas when the number of addition (degree of substitution) of alkylene oxide is small, hydrophilicity decreases. From this viewpoint, the molar substitution degree is preferably 1 or more, and more preferably 2 or more.

The content of the hydroxyalkyl cellulose in the portion where the hydroxyalkyl cellulose is held (the portion where the hydroxyalkyl cellulose permeates) is preferably 0.05 to 3% by mass, more preferably 0.1 to 1.0% by mass, still more preferably 0.1% by mass or more and less than 0.5% by mass, and particularly preferably 0.2% by mass or more and less than 0.5% by mass, based on the mass of the hydrophilic porous membrane.

[ method for producing hydrophilic porous Membrane ]

The hydrophilic porous membrane can be produced by subjecting a porous membrane as a substrate to hydrophilization treatment with hydroxyalkyl cellulose. Specifically, the hydrophilic film can be produced by permeating a hydrophilizing liquid containing hydroxyalkyl cellulose into a porous film. The porous film having the hydrophilized coating layer formed thereon may be further subjected to a cleaning treatment, a sterilization treatment, or the like.

(hydrophilizing solution)

The hydrophilizing solution may be prepared as a solution containing hydroxyalkyl cellulose. The solvent is not particularly limited as long as it is water or a solvent having a property of being miscible with water. The solvent may be a mixed solvent of water and an organic solvent. When a mixed solvent of water and an organic solvent is used, the organic solvent is preferably at least 1 or more lower alcohols. Examples of the lower alcohol include alcohols having 5 or less carbon atoms such as methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, and glycerol. The solvent is more preferably methanol, ethanol, or isopropanol, and still more preferably ethanol.

The hydrophilizing liquid preferably contains 0.005 to 0.500% by mass of hydroxyalkyl cellulose, more preferably 0.200 to 0.490% by mass. By setting the amount to 0.005 mass% or more, hydrophilization of the porous membrane as a base material can be sufficiently performed, and by setting the amount to 0.500 mass% or less, reduction in water permeability due to clogging of the porous membrane can be prevented.

The hydrophilizing liquid may contain a surfactant, a preservative, a film-curing agent such as polyphenol, and the like in addition to the hydroxyalkyl cellulose and the solvent.

(osmosis)

The method of permeating the hydrophilizing liquid into the porous membrane is not particularly limited, and examples thereof include a dipping method, a coating method, a transfer method, and a spraying method.

In order to allow the hydrophilizing liquid to efficiently permeate into the porous membrane, an immersion method or a coating method is preferable. The penetration is preferably performed so that the hydrophilizing liquid penetrates the entire thickness direction of the porous film at least at the site where the hydrophilization is performed.

In the impregnation method, the hydrophilization solution is impregnated into the porous film by impregnating the porous film into the hydrophilization solution. After the immersion, the porous film may be pulled up from the hydrophilizing liquid to remove the excess hydrophilizing liquid.

The impregnation can be carried out under pressure. The hydrophilizing liquid can be efficiently injected into each pore of the porous membrane by pressurization.

The dipping time or pressing time in the dipping treatment or pressing treatment is not particularly limited, and may be generally about 0.5 seconds to 1 minute, and preferably about 0.5 seconds to 30 seconds. The impregnation time can be shortened by selection of a solvent or the like.

The amount of hydroxyalkyl cellulose deposited can be appropriately adjusted depending on the time for which the porous membrane is immersed in the hydrophilizing solution and the concentration of hydroxyalkyl cellulose in the hydrophilizing solution.

When only a part of the porous film is coated, a coating method of coating only a part to be coated with a hydrophilizing liquid can be performed. The coating is preferably performed so that the hydrophilizing liquid penetrates the entire thickness direction of the porous membrane. The application of the hydrophilizing liquid can be performed by a known method such as a method of immersing the hydrophilizing liquid in a sponge or cloth to bring the hydrophilizing liquid into contact with the surface of the porous film, bead coating, gravure coating, or wire bar coating.

(drying and heating)

After the hydrophilization liquid has permeated into the porous film, the solvent in the hydrophilization liquid is preferably removed by drying and volatilization. The drying means is not particularly limited, and air drying or heat drying is preferable in view of simplicity of the production process. Drying can be achieved by simple standing.

(cleaning)

After the above drying, washing is preferably performed using a washing solvent. This is because excess hydroxyalkyl cellulose and the like can be removed. Further, unnecessary components contained in the porous film of the raw material can be removed by washing. The cleaning method is not particularly limited, but the cleaning solvent may be removed by allowing the cleaning solvent to permeate the membrane surface and pore surface of the hydrophilic porous membrane by immersion or press-in method. Examples of the cleaning solvent include solvents exemplified as solvents for hydrophilization solutions. The penetration and removal of the cleaning solvent may be performed 2 or more times. In the washing 2 or more times, the washing solvent may be the same or different, but preferably different. The cleaning solvent used at the end of the cleaning is preferably water. Immersion in water is particularly preferred. This is for removing organic solvent components such as alcohol.

The washed hydrophilic porous membrane is dried again by the above-mentioned steps.

(Sterilization treatment)

As the sterilization treatment of the hydrophilic porous membrane, for example, a high-pressure steam sterilization treatment can be performed. It is particularly preferable to carry out the treatment by high-temperature and high-pressure steam using an autoclave. Generally, the autoclaving treatment of the plastic is performed by pressurizing with saturated steam and performing the treatment for 10 to 30 minutes in an environment of about 110 to 140 ℃. Examples of the autoclave used for the sterilization treatment include SS325 manufactured by TOMY SEIKO co.

< use of hydrophilic porous Membrane >

The hydrophilic porous membrane of the present invention can be used in various applications as a filtration membrane. The filtration membrane is suitable for separation, purification, recovery, concentration, and the like of a liquid containing or suspending various polymers, microorganisms, yeasts, and fine particles, and is particularly suitable for a case where the fine particles are to be separated from a liquid containing the fine particles to be filtered. For example, a filtration membrane can be used for separating fine particles from various suspensions, fermentation solutions, culture solutions, and the like containing fine particles, as well as from pigment suspensions and the like. Specifically, the hydrophilic porous membrane of the present invention can be used as a required microfiltration membrane in the production of pharmaceuticals in the pharmaceutical industry, the production of alcoholic beverages such as beer in the food industry, microfabrication in the field of electronics industry, the production of purified water, and the like.

When the hydrophilic porous membrane of the present invention having a pore size distribution is used as a filtration membrane, the portion having smaller pore sizes is disposed close to the outlet side (outlet side) of the filtrate to perform filtration, whereby fine particles can be efficiently captured. Further, since the hydrophilic porous membrane has a pore size distribution, the fine particles introduced from the surface thereof are removed by adsorption or adhesion before reaching the minimum pore size portion. Therefore, clogging is not likely to occur, and high filtration efficiency can be maintained for a long period of time.

The hydrophilic porous membrane of the present invention can be processed into a shape corresponding to the application and used for various applications. The shape of the hydrophilic porous membrane may be a flat membrane, a tubular shape, a hollow linear shape, a corrugated shape, a fibrous shape, a spherical particle shape, a crushed particle shape, a block continuous shape, or the like. The porous film may be processed into a shape corresponding to the application before hydrophilization treatment of the porous film, or may be processed into a shape corresponding to the application after hydrophilization treatment of the porous film.

The hydrophilic porous membrane may be attached to a sleeve that can be easily detached in a device used for various purposes. The hydrophilic porous membrane is preferably held in the cartridge in a form capable of functioning as a filtration membrane. The cartridge holding the hydrophilic porous membrane can be manufactured in the same manner as a known porous membrane cartridge, and for example, see WO2005/037413 and japanese patent application laid-open No. 2012-045524.

For example, the filter cartridge can be manufactured as follows.

The long hydrophilic porous membrane is pleated so as to have a fold in the short side (width) direction. For example, it is usually sandwiched between 2 membrane holders and can be pleated by a known method. The film support may be a nonwoven fabric, woven fabric, mesh, or the like. The membrane support is used to reinforce the filtration membrane against filtration pressure fluctuations while directing liquid deep into the pleats. The width of the pleats may be, for example, 5mm to 25 mm. Rolling the pleated hydrophilic porous membrane into a cylindrical shape, and sealing the joint.

A cylindrical hydrophilic porous membrane is terminated on the end plate. The end sealing may be performed by a known method depending on the material of the end plate. When a thermosetting epoxy resin is used for the end plate, a liquid of a prepared epoxy resin adhesive is poured into a casting mold to be precured, the viscosity of the adhesive is appropriately increased, and then one end surface of the cylindrical filter material is inserted into the epoxy adhesive and heated to be completely cured. When the material of the end plate is a thermoplastic resin such as polypropylene or polyester, a method of inserting one end surface of the cylindrical filter material into the resin immediately after the hot-melt resin is poured into the mold may be performed. On the other hand, only the sealing surface of the molded end plate may be brought into contact with a hot plate or an infrared heater may be irradiated to melt only the surface of the plate, and one end surface of the cylindrical filter medium may be pressed against the melted surface of the plate to be welded.

The assembled filter cartridge may be further used in a known cleaning process.

In addition, the hydroxyalkyl cellulose in the hydrophilic porous membrane may be partially or completely dissolved in a solvent used in a washing step or the like in the cartridge and removed.

Examples

The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, the amounts used, the ratios, the contents of the processes, the processing steps, and the like shown in the following examples can be appropriately modified within the scope not departing from the gist of the present invention. Therefore, the scope of the present invention should not be interpreted restrictively by the specific examples shown below.

< production of hydrophilic porous membranes in examples and comparative examples >

The hydrophilic polymers described in the table were stirred in water to completely dissolve the hydrophilic polymers, thereby producing hydrophilic liquids having the concentrations described in the table.

As the hydroxypropyl cellulose, hydroxyalkyl cellulose (NISSO hpcm grade, H grade, SL grade or SSL grade) manufactured by NIPPON SODA co.

As the hydroxyethyl cellulose, sansho co., ltd.

As polyvinyl alcohol, product of Sigma-Aldrich co.llc.

The hydrophilizing liquid is permeated into the porous film by an immersion method or a coating method. The impregnation method was performed by continuously immersing the porous membrane in an impregnation tank for the time period shown in table 1. The coating method was performed by applying a coating liquid to the portion of the porous film described in table 1 by a die coating method.

In table 1, PSE20 is FUJIFILM co, polysulfone film PSE20 manufactured by ltd, and PSK45 is FUJIFILM co, polysulfone film PSK45 manufactured by ltd. The PSE20 is a structure with a minimum pore size of 0.2 μm, a thickness of 140 μm and an asymmetric pore size distribution. PSK45 has a minimum aperture of 0.45 μm, a thickness of 170 μm, and an asymmetric aperture distribution structure. Each of the porous films was cut into a size of 25cm × 200 cm.

The infiltrated porous membrane was dried in an oven at 80 ℃ for 80 seconds.

Thereafter, washing is performed in order to remove the excess hydrophilic polymer. The porous membrane was immersed in a normal-temperature ethanol 30% aqueous solution prepared by mixing 3:7 in weight ratio with ethanol and pure water for 30 minutes. Thereafter, the substrate was immersed in pure water for 5 minutes to remove ethanol. Finally, the porous membrane was dried at 70 ℃ under a temperature and humidity environment of 99% for 26 hours, thereby obtaining a hydrophilic porous membrane containing the hydrophilic polymer in an amount shown in table 1.

< evaluation of hydrophilic porous Membrane in examples and comparative examples >

[ evaluation of weight average molecular weight ]

GPC (gel permeation chromatography) measurement was performed under the following analysis conditions to evaluate the weight average molecular weight of the hydrophilic polymer of the raw material.

Column: shodex Ohpak KB805HQ

Mobile phase: 0.1M sodium acetate buffer

Flow rate: 1.0mL/min

Temperature: 40 deg.C

A detector: RI (differential refractometer)

In addition, the molecular weight was calculated using standard Pullulan standards Shodex Pullulan P-5, P-10, P-20, P-50, P-82, P-100, P-200, P-400, P-800, P-1600.

[ integrity test ]

The hydrophilic porous membrane was sandwiched between 2 polypropylene nonwoven fabrics, pleated to a pleat width of 10mm, 138 pleats were taken and rolled into a cylindrical shape, and the joints were welded by an impulse heat sealer. Both ends of the cylinder were cut 5mm each, and the cut surfaces were heat-welded to polypropylene end plates to prepare a filter cartridge having a membrane length of 30 inches.

After the obtained filter cartridge was mounted in a housing and water was passed through the cartridge from the inside toward the outside of the cylinder at 8L/min for 200 seconds, a leak valve at the upper part of the housing was opened to discharge the water in the housing under atmospheric pressure. Subsequently, an air pressure of 150kPa was applied from the water inlet side, and the amount of air (air flow rate) passing through the filter cartridge was measured. From the measurement values, the completeness was evaluated by the following criteria. The results are shown in Table 1.

A:0ml/min to 30ml/min inclusive

B: more than 30ml/min and less than 60ml/min

C: more than 60ml/min and less than 90ml/min

D: more than 90ml/min and less than 300ml/min

E: more than 300ml/min

[ Water permeability ]

The water permeability was evaluated by cutting the hydrophilized porous film from the center region (the region of 10cm at the center of 25cm at the short side and 15cm at the center of 200cm at the long side) into a circular shape having a diameter of 47mm, and applying a pressure of 100kPa to permeate pure water. The volume of water flowing out through the membrane per unit area for 1 minute was determined and used asIs water permeability (ml/min/cm) ² ). At this time, the water permeability was evaluated on the basis of the reduction rate of the water permeability by the hydroxyalkyl cellulose impregnation based on the untreated porous membrane in the following 5 grades. The results are shown in Table 1.

A: more than 0% and less than 15%

B: more than 15 percent and less than 30 percent

C: more than 30 percent and less than 45 percent

D: more than 45 percent and less than 60 percent

E: over 60 percent

[ Table 1]

Claims

1. A hydrophilic porous membrane comprising a porous membrane and hydroxypropyl cellulose retained in the porous membrane,

the porous membrane comprises a polysulfone,

the porous membrane has the following structure: has a pore size distribution in the thickness direction and a pore size distribution which is asymmetric in the thickness direction,

the hydroxypropyl cellulose has a weight average molecular weight of 10,000 or more and less than 110,000,

the content of the hydroxypropyl cellulose is 0.117 to 0.495% by mass relative to the mass of the hydrophilic porous membrane.

2. The hydrophilic porous membrane according to claim 1, wherein,

the hydroxypropyl cellulose has a weight average molecular weight of 10,000 to 100,000.

3. The hydrophilic porous membrane according to claim 1, wherein,

the hydroxypropyl cellulose has a weight average molecular weight of 30,000 to 50,000.

4. The hydrophilic porous membrane according to claim 1, wherein,

the porous membrane retains polyvinylpyrrolidone.

5. The hydrophilic porous membrane according to claim 1, wherein,

the hydroxypropyl cellulose is retained on the entire surface of the porous membrane.

6. The hydrophilic porous membrane according to claim 1, wherein,

the porous membrane has the following structure: has a layered dense site having the smallest pore diameter inside, and the pore diameter continuously increases in the thickness direction from the dense site toward at least one membrane surface of the porous membrane.

7. The hydrophilic porous membrane according to claim 1, wherein,

the minimum pore diameter of the porous membrane is 0.01-10 [ mu ] m.

8. The hydrophilic porous membrane according to claim 1, wherein,

the minimum pore diameter of the porous membrane is 0.2 to 0.45 [ mu ] m.

9. The hydrophilic porous membrane according to any one of claims 1 to 8, wherein,

the porous film is in the form of a long sheet, and the hydroxypropyl cellulose is held only at both ends on the long side.